1. Field of the Invention
This invention relates to apparatus and methods for producing a cursor on a CRT to identify the location of a particular part of a video display. More particularly, this invention relates to techniques for synchronizing cursor signals controlled by a relatively low speed clock with video data clocked at a higher speed.
2. Description of the Prior Art
Video display systems frequently incorporate a so-called RAMDAC to generate the analog signals for controlling the color guns of a CRT. Internally, the RAMDAC operates at a high pixel clock rate such as 135 MHz, and sometimes as high as 360 MHz. U.S. Pat. 4,864,548 shows a system where a cursor generating circuit operating at a relatively low clock rate is synchronized with a RAMDAC operating at a higher clock rate. That system however is quite complex and has problems. One particular problem with that system is that it requires the development of an underflow or carry signal from a multi-bit incremented down-counter to produce a control signal for selecting the pixel location where the cursor pattern is to start.